1. Field of the Invention
This invention relates to particle board binders and is more particularly concerned with the use of organic polyisocyanates as particle board binders, with compositions for said use, and with the particle boards so prepared.
2. Description of the Prior Art
The use is now widely recognized of organic polyisocyanates, particularly toluene diisocyanate, methylenebis(phenyl isocyanate), and polymethylene polyphenyl polyisocyanates, as binders, or as a component or a binder, for the preparation of particle boards; see, for example, U.S. Pat. Nos. 3,428,592; 3,440,189; 3,557,263; 3,636,199; 3,870,665; 3,919,017 and 3,930,110.
In a typical process the binder resins, optionally in the form of a solution or aqueous suspension or emulsion, are applied to or admixed with the particles of cellulosic material, or other types of material capable of forming particle boards, using a tumbler apparatus or blender or other form of agitator. The mixture of particles and binder is then formed into a mat and subjected to heat and pressure using heated platens. The process can be carried out in a batch operation or continuously. To avoid adhesion of the board so formed to the heated platens it has hitherto been necessary to interpose a sheet, impermeable to isocyanate, between the surface of the board and the platen during the forming process, or to coat the surface of the platen, prior to each molding operation, with an appropriate release agent or to coat the surface of the particles themselves with a material which will not adhere to the platen. Any of these alternatives, particularly where the process is being operated on a continuous basis, is cumbersome and a drawback to what is otherwise a very satisfactory method of making a particle board with highly attractive structural strength properties.
I have now found that the above drawbacks to the use of organic isocyanates as particle board binders can be minimized in a very satisfactory manner by incorporating certain phosphinic and or phosphonic acids or derivatives thereof or phosphites as internal release agents in the isocyanate compositions so utilized.
Copending application Ser. No. 134,315 filed Mar. 26, 1980 now U.S. Pat. No. 4,256,995 describes the incorporation of acid phosphates and pyrophosphates as internal release agents in particle board binder compositions based on organic polyisocyanates. Copending application Ser. No. 139,872 filed Apr. 14, 1980 now U.S. Pat. No. 4,257,996 describes the use of related phosphorus compounds for the same purpose.